This invention relates to the removal of soil from fabric in a gaseous environment, and, more particularly, to the utilization of acoustic energy to improve the dislodging of soil from the fabric and to prevent its redeposition onto the fabric.
The dry cleaning of fabrics is currently performed commercially using organic solvents such as perchloroethylene or petroleum derivatives. These solvents pose a health hazard, are smog-producing, and/or are flammable. As an alternative, U.S. Pat. No. 5,467,492 discloses a dry-cleaning process that uses liquid carbon dioxide as a cleaning medium. This process allows the fabric to be cleaned without the use of undesirable chemicals. One of the disadvantages of this liquid carbon dioxide process is that it must be performed within a pressure system, and thus has associated high capital costs.
In an alternative approach, U.S. Pat. No. 5,651,276 describes an apparatus and method to expel soils from fabric using gas jets in an ambient-pressure environment, without immersion of the fabric in a liquid cleaning medium. In this approach, mechanical agitation is provided by a jet of pressurized gas directed at the soiled fabric. The agitation of the fabric, by the mechanical agitation of the pressurized gas and by other coordinated sources of mechanical agitation such as tumbling, loosens and expels particulate soil from the fabric. The soil is entrained in the gas flow and subsequently filtered from the gas flow. The use of gas jet cleaning resolves the health and environmental concerns posed by conventional solvents. An additional benefit is that its use reduces secondary waste streams associated with processes that employ conventional solvents.
These agitation-based processes for cleaning fabric without immersion in water and without the use of environmentally undesirable chemicals have been demonstrated to be operable. Nevertheless, there is a desire to improve their cleaning effectiveness and efficiency. The present invention provides such an improvement.
The present invention provides an improvement to the mechanical agitation process for cleaning fabric such as garments. The modified process has an increased effectiveness and efficiency in removing soil from the fabric, and preventing its redeposition on the fabric. The process remains environmentally friendly, inasmuch as no noxious or dangerous chemicals are used, and waste streams are small. The present approach is compatible with the use of other techniques for enhancing the cleaning process. The process is a xe2x80x9cdry cleaningxe2x80x9d process, and the fabric is not immersed in any liquid cleaning medium during the actual cleaning procedure. The cleaned fabric is dry as it is taken from the cleaning apparatus.
In accordance with the invention, a method for cleaning fabric comprises the steps of providing a piece of fabric having soil therein, providing a source of acoustic energy, and cleaning the piece of fabric in a gaseous environment wherein the piece of fabric is not immersed in a liquid cleaning medium. The step of cleaning includes the steps of subjecting the piece of fabric to acoustic energy emitted from the source of acoustic energy, and, simultaneously, mechanically agitating the piece of fabric. The piece of fabric is preferably mechanically agitated by a jet of a soil-dislodging gas and/or by tumbling. All or a part of the piece of fabric may be treated with a mobilizing chemical that loosens the soil.
The frequency of the acoustic energy may be either in an audible range or at a high acoustic frequency. Typically, the acoustic energy has a frequency of from about 1 hertz up to about 1 megahertz (106 hertz). This acoustic energy is preferably provided by an acoustic device which converts an electrical input signal into an acoustic output signal. There is typically an electrical source which provides the electrical input signal to the acoustic device. The electrical source may include a controllable function generator which provides the electrical input signal to the acoustic device.
Simultaneously with the subjecting of the fabric to the acoustic energy, it is mechanically agitated by any operable approach. Examples of operable mechanical agitation techniques include gas jet agitation and tumbling agitation. In the first case, the jet of the soil-dislodging gas loosens soil that adheres to the fibers of the fabric, both by direct impingement and by causing flexure in the fabric that frees the soil from the fabric. In the second case, tumbling as in a cylindrical drum causes the fabric to flex, having somewhat the same effect. The acoustic energy creates sympathetic vibrations in the fibers, which aid in and accelerate this loosening and dislodging of the soil from the fabric at the same time that it is mechanically agitated.
The fabric may be treated with safe, environmentally benign chemicals to improve the dislodging process. Such chemicals may serve to loosen particulate soil, or to cause non-particulate soil to become particulated. The chemicals may be generally acting chemicals that are used to treat the entire fabric, or xe2x80x9cspottingxe2x80x9d chemicals that act on specific types of soil. Such chemicals may be applied either before or during the cleaning operation. Other chemicals such as odorants and anti-static compounds may be introduced during or after the cleaning operation. The chemicals are selected to be environmentally friendly and non-toxic.
This method of the invention is a gaseous approach, accomplished without the immersion of the fabric in a liquid cleaning medium while it is subjected to the acoustic energy. This feature is important, inasmuch as the fabric is dry and ready for use immediately after cleaning is complete. The present approach may therefore be considered a dry-cleaning process, as distinct from a washing process wherein the fabric is immersed in a bath of a liquid cleaning medium, as in conventional tub washing of fabric in water. In the present approach, the fabric may be contacted with a liquid or even immersed in a liquid prior to the step of subjecting the fabric to acoustic energy, but it may not be immersed in a liquid during and simultaneously with the step of subjecting the fabric to acoustic energy.
The present approach provides a technique for dry-cleaning fabrics. The approach has enhanced effectiveness as compared with conventional techniques, and as compared with prior gas jet cleaning techniques. The acoustic energy vibrates the fabric to aid in the dislodging of soil from the fabric, and that same vibration aids in preventing redeposition of the soil back onto the fabric before the soil may be removed from the system, as by filtering. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.